As a result of blasting operations, I-T-H drill string components (usually pipe) are frequently damaged and, as a consequence, become stuck in the drill hole. Depending on the length of the pipe, considerable economic losses may be experienced when the entire drill string cannot be retrieved simply because a small portion has become stuck. It is difficult and sometimes impossible to uncouple drill pipe joints above the damaged section at any appreciable depth. Assignee looses several $100,000 a year in abandoned but otherwise good drill pipe.
There have been attempts to wrestle with this problem. Pipe cutters and perforators of various descriptions have been devised. Principally, a cutter of some description is utilized. Although perhaps effective for conventional pipe cutting operations and on the surface, they are unwieldily when applied to I-T-H pipe and inapplicable at great depths.
Representative designs may be found in U.S. Pat. Nos. 514,985; 669,983; 1,088,135; 4,220,201; 4,307,512; 4,527,511; 4,574,672; German Auslegeschrift No. 1,136,956; German Patentschrift No. 342,498 and Russian No. 605,934.
Clearly an apparatus especially addressed to the unique demands of the retrieval of non-damaged I-T-H pipe is desirable.